All SSL configuration is done per-storage.
To pin the certificate by fingerprint:
[storage foo] type = "caldav" ... verify_fingerprint = "6D:83:EA:32:6C:39:BA:08:ED:EB:C9:BC:BE:12:BB:BF:0F:D9:83:00:CC:89:7E:C7:32:05:94:96:CA:C5:59:5E"
SHA256-Fingerprints must be used, MD5 and SHA-1 are insecure and not supported. CA validation is disabled when pinning a fingerprint.
You can use the following command for obtaining a SHA256 fingerprint:
echo -n | openssl s_client -connect unterwaditzer.net:443 | openssl x509 -noout -fingerprint -sha256
However, please consider using Let's Encrypt such that you can forget about all of that. It is easier to deploy a free certificate from them than configuring all of your clients to accept the self-signed certificate.
To point vdirsyncer to a custom set of root CAs:
[storage foo] type = "caldav" ... verify = "/path/to/cert.pem"
Vdirsyncer uses the aiohttp library, which uses the default `ssl.SSLContext https://docs.python.org/3/library/ssl.html#ssl.SSLContext`_ by default.
There are cases where certificate validation fails even though you can access
the server fine through e.g. your browser. This usually indicates that your
installation of python or the aiohttp or library is somehow broken. In
such cases, it makes sense to explicitly set verify or
verify_fingerprint as shown above.
Client certificates may be specified with the auth_cert parameter. If the
key and certificate are stored in the same file, it may be a string:
[storage foo] type = "caldav" ... auth_cert = "/path/to/certificate.pem"
If the key and certificate are separate, a list may be used:
[storage foo] type = "caldav" ... auth_cert = ["/path/to/certificate.crt", "/path/to/key.key"]